DIAC is a four-letter acronym that may stand for:

• DIode for Alternating Current, a bidirectional trigger diode
• Department of Immigration and Citizenship, an Australian government department
• Dental Industry Association of Canada
• Disability Information & Advice Centre, a British charity
• Design Industry Advisory Committee
• Defense Intelligence Analysis Center, the former name of the Defense Intelligence Agency Headquarters
• Dubai International Academic City

• Melonhead
• Melon head
• Melonheads
• Melon heads
• Melonie Diaz
• Meloni Thawne
• Melon Kinen-Bi
• Melon pan
• Melon pear
• Melon vine borer
• Melonycteris
• Melonycteris aurantius
• Melonycteris melanops
• Melonycteris woodfordi
• Melony G. Griffith
• Meloodia
• Melophus
• Melophus lathami
• Melopsittacini
• Melopyrrha
• Melopyrrha nigra
• Melor
• Melora (DS9 episode)
• Melora Harte
• Melora Walters