WordNet sense 1 (express recognition of the presence or existence of, or acquaintance with):

notice

WordNet sense 2 (report the receipt of):

receipt

WordNet sense 3 (express obligation, thanks, or gratitude for):

recognize, recognise

WordNet sense 4 (declare to be true or admit the existence or reality or truth of):

admit

WordNet sense 5 (accept (someone) to be what is claimed or accept his power and authority):

know