"This pond's water is cold."
Translation:इस तालाब का पानी ठंडा है।
In your examples, cold is an adjective in both cases. Cold can be a noun as in, "My cat always sits in the sun. He hates the cold." In the original sentence, ठंडा is also an adjective. It describes a noun (the pond water). According to my Hindi-speaking husband, ठंडा is chilly, while ठंड is cold.
Ya. That was probably a bad example on my part.
But ठंड is the noun corresponding to the adjective ठंडा. (Such noun forms can be used with the verb लगना in Hindi while English would expect adjectives. The sentence 'mujhe thand lagi' may be literally translated to something like 'To me, coldness is felt' though it means 'I felt cold').
Your sentence would be translated 'मेरी बिल्ली हमेशा धूप में बैठती है। उसे ठंड से नफ़रत है।'