• aoft x-ray,
• zoft x-ray,
• xoft x-ray,
• doft x-ray,
• eoft x-ray,
• woft x-ray,
• sift x-ray,
• skft x-ray,
• slft x-ray,
• spft x-ray,
• s0ft x-ray,
• s9ft x-ray,
• sodt x-ray,
• soct x-ray,
• sovt x-ray,
• sogt x-ray,
• sott x-ray,
• sort x-ray,
• sofr x-ray,
• soff x-ray

The adjective form of "soft x-ray" is "soft x-ray". In English, it is common to use the same word for both the noun and adjective forms in scientific terminology.

The plural form of "soft x-ray" is "soft x-rays".

The singular form of the word "soft x-ray" is "soft x-ray". The word does not change when it is in singular form.