1. The act of prolonging something
   - prolongation, protraction, perpetuation

1. Make longer
   "Lengthen this skirt, please" 
2. Become long or longer
   "In Spring, the days lengthen"

Type of: continuance, continuation, grow, increase

Antonym: shorten

• order Arales
• order Araneae
• order Araneida
• order Aristolochiales
• order arms
• order Artiodactyla
• order Aspergillales
• order Auriculariales
• order Batoidei
• order Batrachia
• order Belemnoidea
• order Bennettitales
• order Berycomorphi
• order Blastocladiales
• order book
• order Branchiura
• order Bryales
• order Campanulales
• order Caprimulgiformes
• order Carnivora
• sorority
• sorption
• sorrel
• sorrel tree
• sorrily