The most common and most likely answer to this crossword clue is the 5 letter word BASIC
I've seen this crossword clue in The Times
B
A
S
I
C
More clues leading to the result BASIC
- Essential one Conservative supports party, mostly
- Vanilla ice, shrinking by degrees
- Degree thus simple?
- Lowest degree, like that
- No-frills airline with complaint cut short
- Fundamental part of fabric is absent, on reflection
- Cardinal is in taxi for return journey
- Fundamental, thus to support rise of upper classes
- Plain is one, in degrees Celsius
- Simple precis, abridged, shows up
Buddy explains!

The straight part
We know that "Lowest" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lowest = basic.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 BASIC mean?
BASIC noun- A necessary commodity, a staple requirement.
- An elementary building block, e.g. a fundamental piece of knowledge.
- Basic training.
- Necessary, essential for life or some process.
- Elementary, simple, fundamental, merely functional.
- Of or pertaining to a base; having a pH greater than 7.
- Unremarkable or uninteresting; boring; uncool.