Visitors ignoring temperature estimate (5)
I believe the answer is:
guess
'estimate' is the definition.
(synonyms)
'visitors ignoring temperature' is the wordplay.
'visitors' becomes 'guests' (guest is a kind of visitor).
'ignoring' suggests deleting specific letters.
'temperature' becomes 't' (abbreviation).
'guests' with 't' taken out is 'GUESS'.
(Other definitions for guess that I've seen before include "Estimate on the basis of little information" , "Hypothesis" , "Reckon" , "Speculate" , "Imagine" .)