"of or pertaining to a particular occupation, calling, or trade," 1850, from occupation + -al (1). Occupational therapy is attested by 1918; occupational risk by 1951. Related: Occupationally.
"to pledge, engage by solemn promise" (obsolete except in archaic plight one's troth), Middle English plighten, from Old English pligtan, plihtan "to endanger, imperil, compromise," verb form of pliht (n.) "danger, risk" (see plight (n.2)), from Proto-Germanic *plehti-, which ultimately is perhaps from PIE root *dlegh- "to engage oneself, be or become fixed," or else a substratum word. The notion is "to put (something -- honor, troth) in danger or risk of forfeiture;" it is rarely used of physical things. Related: Plighted; plighting.
"inner membrane in the stomach of an unweaned calf or other animal," used for making cheese, etc.; also the mass of curdled milk found in the stomach, mid-15c., probably from an unrecorded Old English *rynet, related to gerennan "cause to run together," because it makes milk run or curdle; from Proto-Germanic *rannijanan, causative of *renwanan "to run" (from PIE root *rei- "to run, flow"). Compare German rinnen "to run," gerinnen "to curdle." Hence, "anything used to curdle milk."