Add to workers in holiday month with our lot off (7)
I believe the answer is:
augment
'add to' is the definition.
(thesaurus)
'workers in holiday month with our lot off' is the wordplay.
I cannot really understand how this works, but
'workers' could be 'men' (man is a kind of worker) and 'men' is found in the answer.
'month' could be 'aug' (Aug is an example) and 'aug' is found within the answer.
A single letter 't' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
(Other definitions for augment that I've seen before include "Supplement" , "Make greater in size, number, etc." , "Swell" , "boost" , "Add to, increase" .)