tečnost

1. liquid; fluid
   Po ovoj vrućini pijte što više tečnosti. — In this heat, drink as much fluid as you can.
   U ručnom prtljagu tečnosti smeju da budu samo u bočicama do sto mililitara. — In hand luggage, liquids are only allowed in containers of up to a hundred millilitres.
2. (of speech, language) fluency
   Gramatiku znam, ali mi fali tečnost u govoru. — I know the grammar, but I lack fluency when I speak.

In Serbia the usual word for "liquid" is tečnost rather than the Croatian tekućina.