• auboptimal,
• zuboptimal,
• xuboptimal,
• duboptimal,
• euboptimal,
• wuboptimal,
• syboptimal,
• shboptimal,
• sjboptimal,
• siboptimal,
• s8boptimal,
• s7boptimal,
• suvoptimal,
• sunoptimal,
• suhoptimal,
• sugoptimal,
• subiptimal,
• subkptimal,
• sublptimal,
• subpptimal

• submerge,
• substation,
• subcontract,
• optimal,
• subtotal,
• subjective,
• substitute,
• subsidy,
• subtract,
• submissive,
• subtle,
• subsequent,
• subordinate,
• submarine,
• suburb.

The adjective form of the word "suboptimal" is "suboptimal".

The plural form of the word "suboptimal" is "suboptimals." However, it is worth noting that "suboptimal" is typically used as an adjective rather than a noun, so the need for a plural form may be rare.

The singular form of the word "suboptimal" is "suboptimum".