Under no circumstances; not at all. It is used to strongly negate a statement or to emphasize that something is not true.
example
Ich bin keineswegs müde, wir können gerne noch bleiben.
I am by no means tired; we can gladly stay a bit longer.
Usage tips
Word structure
The word is made up of 'keines' and 'Weges' (an old genitive form of 'Weg', meaning way). Literally, it means 'in no way whatsoever.'
EXAMPLE
Das Ergebnis war keineswegs das, was wir erwartet hatten.
The result was by no means what we had expected.
Word order
'Keineswegs' (by no means) can stand at the beginning of a sentence in position 1. Then the conjugated verb follows directly after it. It can also stand after the verb in the middle of the sentence.
EXAMPLE
Keineswegs wollte ich Sie damit beleidigen.
By no means did I intend to offend you with that.
Register
'Keineswegs' (by no means) belongs more to written language or a more formal style. It is a strong and emphatic form of negation.
EXAMPLE
Ihre Bedenken sind keineswegs unbegründet.
Your concerns are by no means unfounded.
Compare with
near_synonym
keineswegs vs nichts
nothing
'nichts' and 'keineswegs' can both negate a statement, but they do it in different ways. 'nichts' means that no thing is there or no thing happens. 'keineswegs' strongly negates an entire statement and means something like 'not at all'. It sounds somewhat more formal or emphatic than simple 'nicht' (not). So you say 'Ich habe nichts gehört' (I heard nothing / I didn’t hear anything) when there is no information. You say 'Das ist keineswegs sicher' (That is by no means certain) when you are clearly contradicting a statement.
keineswegs
In der Werkstatt ist Frau Kaya keineswegs zufrieden mit der Reparatur.
At the repair shop, Ms. Kaya is by no means satisfied with the repair.
nichts
Meine Nachbarin hat beim Termin nichts Neues erfahren.
My neighbor didn’t learn anything new at the appointment.