diff --git a/channeld/full_channel.h b/channeld/full_channel.h
index 67a1f3a1b..d51d8e202 100644
--- a/channeld/full_channel.h
+++ b/channeld/full_channel.h
@@ -105,7 +105,7 @@ enum channel_add_err {
  * @cltv_expiry: block number when HTLC can no longer be redeemed.
  * @payment_hash: hash whose preimage can redeem HTLC.
  * @routing: routing information (copied)
- * @htlcp: optional pointer for resulting htlc: filled in iff CHANNEL_ERR_NONE.
+ * @htlcp: optional pointer for resulting htlc: filled in if and only if CHANNEL_ERR_NONE.
  *
  * If this returns CHANNEL_ERR_NONE, the fee htlc was added and
  * the output amounts adjusted accordingly.  Otherwise nothing
@@ -148,7 +148,7 @@ enum channel_remove_err {
  * @channel: The channel state
  * @owner: the side who offered the HTLC (opposite to that failing it)
  * @id: unique HTLC id.
- * @htlcp: optional pointer for failed htlc: filled in iff CHANNEL_ERR_REMOVE_OK.
+ * @htlcp: optional pointer for failed htlc: filled in if and only if CHANNEL_ERR_REMOVE_OK.
  *
  * This will remove the htlc and credit the value of the HTLC (back)
  * to its offerer.
diff --git a/common/bolt11.h b/common/bolt11.h
index 5336aadcc..9347116f2 100644
--- a/common/bolt11.h
+++ b/common/bolt11.h
@@ -42,7 +42,7 @@ struct bolt11 {
 	struct sha256 payment_hash;
 	struct pubkey receiver_id;
 
-	/* description_hash valid iff description is NULL. */
+	/* description_hash valid if and only if description is NULL. */
 	const char *description;
 	struct sha256 *description_hash;
 
diff --git a/common/daemon_conn.c b/common/daemon_conn.c
index 0928b84b6..fe6abcd18 100644
--- a/common/daemon_conn.c
+++ b/common/daemon_conn.c
@@ -57,7 +57,7 @@ bool daemon_conn_sync_flush(struct daemon_conn *dc)
 	}
 	io_fd_block(daemon_fd, false);
 
-	/* Success iff we flushed them all. */
+	/* Success if and only if we flushed them all. */
 	return msg == NULL;
 }
 
diff --git a/common/dev_disconnect.c b/common/dev_disconnect.c
index f507b332e..3a2599cd9 100644
--- a/common/dev_disconnect.c
+++ b/common/dev_disconnect.c
@@ -12,7 +12,7 @@
 #include <wire/gen_peer_wire.h>
 
 #if DEVELOPER
-/* We move the fd IFF we do a disconnect. */
+/* We move the fd if and only if we do a disconnect. */
 static int dev_disconnect_fd = -1;
 static char dev_disconnect_line[200];
 static int dev_disconnect_count, dev_disconnect_len;
diff --git a/common/wire_error.h b/common/wire_error.h
index 23dd2b4cc..e33533374 100644
--- a/common/wire_error.h
+++ b/common/wire_error.h
@@ -48,7 +48,7 @@ bool channel_id_is_all(const struct channel_id *channel_id);
  *
  * @ctx: context to allocate from
  * @errmsg: the wire_error
- * @channel: (out) channel it's referrring to, or NULL if don't care.
+ * @channel: (out) channel it's referring to, or NULL if don't care.
  */
 char *sanitize_error(const tal_t *ctx, const u8 *errmsg,
 		     struct channel_id *channel_id);
diff --git a/external/libwally-core/src/secp256k1/src/group.h b/external/libwally-core/src/secp256k1/src/group.h
index 4957b248f..706ffd92f 100644
--- a/external/libwally-core/src/secp256k1/src/group.h
+++ b/external/libwally-core/src/secp256k1/src/group.h
@@ -45,7 +45,7 @@ static void secp256k1_ge_set_xy(secp256k1_ge *r, const secp256k1_fe *x, const se
 
 /** Set a group element (affine) equal to the point with the given X coordinate
  *  and a Y coordinate that is a quadratic residue modulo p. The return value
- *  is true iff a coordinate with the given X coordinate exists.
+ *  is true if and only if a coordinate with the given X coordinate exists.
  */
 static int secp256k1_ge_set_xquad(secp256k1_ge *r, const secp256k1_fe *x);
 
diff --git a/external/libwally-core/src/secp256k1/src/group_impl.h b/external/libwally-core/src/secp256k1/src/group_impl.h
index 18f2b3735..28c8c1248 100644
--- a/external/libwally-core/src/secp256k1/src/group_impl.h
+++ b/external/libwally-core/src/secp256k1/src/group_impl.h
@@ -641,7 +641,7 @@ static int secp256k1_gej_has_quad_y_var(const secp256k1_gej *a) {
     }
 
     /* We rely on the fact that the Jacobi symbol of 1 / a->z^3 is the same as
-     * that of a->z. Thus a->y / a->z^3 is a quadratic residue iff a->y * a->z
+     * that of a->z. Thus a->y / a->z^3 is a quadratic residue if and only if a->y * a->z
        is */
     secp256k1_fe_mul(&yz, &a->y, &a->z);
     return secp256k1_fe_is_quad_var(&yz);
diff --git a/lightningd/chaintopology.c b/lightningd/chaintopology.c
index 905c709f9..96df5fc16 100644
--- a/lightningd/chaintopology.c
+++ b/lightningd/chaintopology.c
@@ -140,7 +140,7 @@ struct txs_to_broadcast {
 	/* These are hex encoded already, for bitcoind_sendrawtx */
 	const char **txs;
 
-	/* Command to complete when we're done, iff dev-broadcast triggered */
+	/* Command to complete when we're done, if and only if dev-broadcast triggered */
 	struct command *cmd;
 };
 
diff --git a/wallet/wallet.h b/wallet/wallet.h
index f1794d873..1741b04db 100644
--- a/wallet/wallet.h
+++ b/wallet/wallet.h
@@ -91,7 +91,7 @@ struct wallet_payment {
 	enum wallet_payment_status status;
 	struct pubkey destination;
 	u64 msatoshi;
-	/* Iff PAYMENT_COMPLETE */
+	/* If and only if PAYMENT_COMPLETE */
 	struct preimage *payment_preimage;
 	struct secret *path_secrets;
 };