Female, one entering pub with tense baby (6)
I believe the answer is:
infant
'baby' is the definition.
(I know that baby can be written as infant)
'female one entering pub with tense' is the wordplay.
'female' becomes 'fa' (I've seen this in other clues).
'one entering' means one lot of letters goes inside another.
'pub' becomes 'inn' (an inn is a type of pub).
'with' means one lot of letters go next to another.
'tense' becomes 't' (grammatical abbreviation).
'fa' going into 'inn' is 'infan'.
'infan'+'t'='INFANT'
(Other definitions for infant that I've seen before include "Very young child or baby" , "Thing in early stage; minor (legal)" , "Small baby" , "Child at an early stage of life" , "Very small child" .)