noun, noun which may take the genitive case particle 'no'
long and uninterrupted; unbroken; continuous
Emphasizes something continuing without a break, often used for abstract things like traditions, efforts, or lines of thought.
This tradition has been passed down unbroken for generations.
連綿不断の努力が実を結んだ。
Continuous effort bore fruit.
連綿 alone also means 'unbroken' or 'continuous', but 連綿不断 is a more emphatic four-character compound.
不断 means 'constant' or 'unceasing', and is used in compounds like 不断の努力 (constant effort).
A yojijukugo (four-character compound) combining 連綿 (unbroken, continuous) and 不断 (constant, unceasing). The exact historical derivation is uncertain, but the meaning is transparent from its components.