5050 ÷ 1 close to infinity? That's remote (6)
I believe the answer is:
lonely
'remote' is the definition.
(lonely can mean remote or isolated)
'5050 1 close to infinity?' is the wordplay.
I cannot really see how this works, but
'1' could be 'one' (synonyms) and 'one' is found in the answer.
'5050' could be 'll' (two Ls, Roman numerals for 50) and 'll' is found within the leftover letters.
A single letter 'y' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'that's' is the link.
(Other definitions for lonely that I've seen before include "'I wandered ..... as a cloud' Wordsworth )" , "Unfrequented" , "Solitary, lacking company" , "Forlorn, solitary" , "Without companions" .)