Seemingly rational little gap in record (7)
I believe the answer is:
tenable
'seemingly rational' is the definition.
'little gap in record' is the wordplay.
'little gap' becomes 'en' (typographical space as wide as an 'n').
'in' means one lot of letters goes inside another.
'record' becomes 'table' (I've seen this before).
'en' placed into 'table' is 'TENABLE'.
(Other definitions for tenable that I've seen before include "Of argument, rational and defensible" , "Viable" , "possible to maintain" , "Based on sound reasoning or evidence" , "Able to be held" .)