This is the 985th most frequent Icelandic word.
fela
To hide.
Here, 'fela' is used as a verb meaning 'to hide.'
Ég ætla að fela bréfið undir rúminu.
I am going to hide the letter under the bed.
In this sentence, 'fela sig' (reflexive form) means 'to hide oneself.'
Hún var góð í að fela sig í feluleiknum.
She was good at hiding herself in hide-and-seek.
The word 'fela' here is used in the sense of concealing or withholding.