Pensive debut for 'Who's On First Base' - missing second part of routine (7)
I believe the answer is:
wistful
'pensive' is the definition.
(I know that pensive can be written as wistful)
'debut for who's on first base missing second part of routine' is the wordplay.
I cannot really understand how this works, but
'first' could be 'ist' (ist resembles 1st) and 'ist' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for wistful that I've seen before include "Regretfully longing" , "Melancholy" , "Sadly pensive" , "(Of a smile) showing vague or regretful longing" , "Disconsolate" .)