momentary意思是“瞬刻的”、“暂时的”(transitory or lasting only for a moment),其后常跟pain、interruption、expectation、happiness、emotion等词,其同义词是transient/ephemeral;反义词是lasting.
momentous意思是“重大的“(of great consequence)。其后常跟events、news、moments、date等词,其同义词是important、highly significant;反义语是trifling。