Feminine of 'amen; something fixed, i.e. A covenant. An allowance -- certain portion, sure.
see HEBREW 'amen
H548. amanah
אֲמָנָה noun feminine faith, support.
1 אֲמָנָה כֹּרְתִים אֲנַחְנוּ we are plighting faith (make a sure covenant AV RV) Nehemiah 10:1.
2 ׳א המ ׳עַל support, fixed provision, for the singers Nehemiah 11:23.