The most common and most likely answer to this crossword clue is the 6 letter word PRIMER
I've seen this crossword clue in The Times
P
R
I
M
E
R
More clues leading to the result PRIMER
- Textbook's protective cover
- Textbook device for detonating charge
- Textbook of the highest quality by foremost of rabbis
- Royal put on proper coat
- Base coat for a skirting edge
- Margin used in a preparatory textbook
- Hesitation after proper introduction
- Introductory textbook, gloss over it perhaps?
- Demure queen’s first coat
- Coat initially put on demure monarch
Buddy explains!

The straight part
We know that "Textbook/protective cover" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case textbook/protective cover = primer.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PRIMER mean?
PRIMER noun- A prayer or devotional book intended for laity, initially an abridgment of the breviary and manual including the hours of the Virgin Mary, 15 gradual and 7 penitential psalms, the litany, the placebo and dirige forming the office of the dead, and the commendations.
- Similar works issued in England for private prayer in accordance with the Book of Common Prayer.
- A children's book intended to teach literacy: how to read, write, and spell.
- An introductory text on any subject, particularly basic concepts.
- An elementary school class; an elementary school student.
- Any substance or device, such as priming wire or blasting cap, used to ignite gunpowder or other explosive.
- A person who primes explosives.
- A substance used to prime wood, metal, etc. in preparation for painting.
- A layer of such a substance.
- A layer of makeup that goes beneath the foundation; undermakeup.
- A person who primes wood, metal, etc.
- A molecule which initiates the synthesis of an enzyme, a single-stranded nucleic acid molecule which initiates DNA replication.
- A pheromone which interacts first with the endocrine system.
- A device used to prime an internal combustion engine with gasoline, in airplanes.
- A person who prunes trees.
- First in time, initial, early.
- First in importance, premier.
- First in position, foremost.