Curious numbers close to infinity (4)
I believe the answer is:
nosy
'curious' is the definition.
('nosy' can be similar in meaning to 'curious')
'numbers close to infinity' is the wordplay.
'numbers' becomes 'nos' (no. is a kind of number**).
'close to' suggests the final letters (the close/ending of).
The final letter of 'infinity' is 'y'.
'nos'+'y'='NOSY'
(Other definitions for nosy that I've seen before include "Fragrant" , "Showing too much curiosity about people's affairs" , "lots of questions" , "Meddlesome" , "Inquisitive in nasal manner" .)