các

See also: Appendix:Variations of "cac"

Tày

Ultimately from Chinese 閣 / 阁 (gé).

các (角, 阁)

Ultimately from Chinese 各.

các (各)

Ultimately from Chinese 擱 / 搁.

các

to place something against something
các slảo phjác slửa ― to hang a clothes-drying pole

mừ các phjác ― hands placed on the forehead

bấu ngần, bấu chèn kha các pha ― (please add an English translation of this usage example)
to place something to reach something up high
Synonym: cái

các đuây ― to place a ladder

Lương Bèn (2011) Từ điển Tày-Việt [Tay-Vietnamese dictionary]‎ (in Vietnamese), Thái Nguyên: Nhà Xuất bản Đại học Thái Nguyên
Lục Văn Pảo, Hoàng Tuấn Nam (2003) Hoàng Triều Ân, editor, Từ điển chữ Nôm Tày [A Dictionary of (chữ) Nôm Tày]‎ (in Vietnamese), Hanoi: Nhà xuất bản Khoa học Xã hội
Léopold Michel Cadière (1910) Dictionnaire Tày-Annamite-Français [Tày-Vietnamese-French Dictionary]‎ (in French), Hanoi: Impressions d'Extrême-Orient

Sino-Vietnamese word from 各 (“each, individually, every, all”).

các

Not used very often in colloquial Vietnamese, replaced by mấy, except in pronouns (such as các bạn). Even then, the use of these pronouns might indicate that the speaker wants to sound serious.
Generally speaking, các suggests that all of a given set of entities are involved, as opposed to những, which implies that only a certain number of the total possible number are referred to.
Plural marking is not always grammatically required in Vietnamese, in contrast with many Indo-European languages, and can be omitted in many situations.