Unenthusiastic old learner joining company (4)
I believe the answer is:
cool
'unenthusiastic' is the definition.
(I've seen this before)
'old learner joining company' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'joining' says to put letters next to each other.
'company' becomes 'co' (abbreviation).
'o'+'l'='ol'
'ol' after 'co' is 'COOL'.
(Other definitions for cool that I've seen before include "Relaxed; not warm" , "Neither warm nor very cold" , "Unemotional or trendy" , "Quite cold" , "Fashionably attractive" .)