This is the 10473rd most frequent Polish word.
czêsto
"Often."
'Nieczęsto' is a negation of 'często,' used here to describe a rarely occurring event, in this case, meeting old friends.
Nieczęsto spotykamy się z dawnymi przyjaciółmi.
We don't often meet with old friends.
'Często' is used as an adverb modifying the verb 'odwiedzam' (visit) to indicate the frequency of the action.
Często odwiedzam bibliotekę, ponieważ lubię czytać.
I frequently visit the library because I like to read.
'Często' is applied here to modulate the adjective 'trudno' (difficult), conveying the frequency of difficulty encountered.