simultaneous (adj.)
- accessory
- accompanying
- attendant
- coetaneous
- coeval
- coexistent
- coexisting
- coincident
- coinciding
- collateral
- combined
- concomitant
- concurrent
- concurring
- conjoint
- contemporaneous
- contemporary
- conterminous
- correlative
- coterminous
- coupled
- fellow
- isochronal
- isochronous
- joined
- joint
- mutual
- paired
- parallel
- synchronal
- synchronic
- synchronous
- twin
