21-letter words containing h, y, p, n
- reverse polish syntax — postfix notation
- schlieren photography — a type of photography which records schlieren
- snappy video snapshot — (hardware) (registered trademark) A frame grabber for the IBM PC designed and marketed by Play, Inc..
- sympathetic vibration — a vibration induced by resonance.
- symphonie fantastique — a programmatic symphony (1830–31) in five movements by Hector Berlioz.
- therapeutic community — a group-based form of therapy for mental disorders, sometimes residential
- third-party insurance — insurance that compensates for a loss to a party other than the insured for which the insured is liable.