- 4-methylpyridine
- 4-nitroaniline
- 4-nitrophenol
- 4-poster
- 4-tert-butylcatechol
- 4-tert-butylphenol
- 4130 steel
- 45 nm
- 4G
- 4T1
- 4th dimension
- 5-HT receptor
- 5-fluorouracil
- 5-hydroxyindoleacetic acid
- 5-hydroxymethylcytosine
- 5-hydroxytryptophan
- 5-methylcytosine
- 500 kHz
- 5052 aluminium alloy
- 5083 aluminium alloy
- 5G
- 5G NR
- 5G network slicing
- 5S rRNA
- 6-APA
- 6-phosphogluconate dehydrogenase
- 6061 aluminium alloy
- 6063 aluminium alloy
- 64-bit computing
- 65 nm
- 6LoWPAN
- 6PPD
- 7-ACA
- 7-dehydrocholesterol
- 7075 aluminium alloy
- 8-aminoquinoline
- 8-bit color
- 8-oxo-2'-deoxyguanosine
- 8-oxoguanine
- 90 nm
- A limit cycle
- A limit set
- A priori
- A priori and a posteriori
- A simplicial complex
- A* search algorithm
- A-DNA
- A-Train
- A-VSB
- A-frames