ON (adj)  In operation  MAKE SURE THE BATTERIES ARE ON.  
 ON (adv)  1. In operation  MAKE SURE THAT THE XXXX LIGHT COMES ON.  
    2. In "contact"  PUT ON PROTECTIVE CLOTHING.  
 ON (pre)  Function word that shows "contact, support, direction"  PUT THE XXXX ON THE SUPPORT FITTING.  
 once (adv)  ONE TIME  PUSH THE PUSHBUTTON SWITCH ONE TIME.  Press pushbutton switch once.
 once (con)   WHEN  WHEN THE UNIT IS ON ITS MOUNTING, LOCK IT.  Once the unit is on its mounting, it can be locked.
 ONE (n)  That refers to a "single" person or object  IF THE LABEL IS NOT THERE, ATTACH A NEW ONE.  
 ONLY (adj)  "Nothing" more or different  THIS IS THE ONLY APPROVED CONFIGURATION.  
 ONLY (adv)  "Exclusively"  TO TIGHTEN THE NUTS, USE ONLY A TORQUE WRENCH.  
onto (pre)  ON  PUT THE TRANSCEIVER ON ITS MOUNTING TRAY.  Place the transceiver onto its mounting tray.
 opaque (adj)  NOT TRANSPARENT  USE A XXXX TO CLEAN THE PLASTIC SURFACES THAT ARE NOT TRANSPARENT.  Use a XXXX to clean opaque plastic surfaces.
 OPEN (adj)  That lets something go in or out  PUT A PLUG ON THE OPEN ENDS OF THE PIPES.  
 OPEN (v),
 OPENS, OPENED, OPENED  1. To move from the closed position  OPEN THE PRESSURE VALVE.  
    2. To operate a circuit breaker to "interrupt" an electrical circuit (TN)  OPEN, TAG, AND SAFETY THE CIRCUIT BREAKER.