Meaning a number will get left out (7)
I believe the answer is:
portent
'meaning a number' is the definition.
'portent' can be an answer for 'meaning' (thesaurus). I'm not certain of the 'a number' bit.
'will get left out' is the wordplay.
'will get' becomes 'ten' (I can't justify this - if you can you should give a lot more credence to this answer).
'left' becomes 'port' (left side of a ship - opposite of starboard).
'out' indicates putting letters inside.
'ten' put inside 'port' is 'PORTENT'.
Can you help me to learn more?
(Other definitions for portent that I've seen before include "Evil omen" , "bad sign" , "Sign of thing to come" , "Sign, omen" , "Prophetic sign" .)