Final answer:
The subject is likely 'lagger,' which can serve as both a noun and adjective to describe someone who is behind or something that is sluggish, respectively.
Step-by-step explanation:
The definition of a term that has both noun and adjective forms, which are synonymous with 'slowpoke' and 'straggler' in the noun form, and 'sluggish' in the adjective form. The antonyms provided for the noun form are 'early bird,' and for the adjective form, the antonyms are 'swift,' 'speedy,' and 'prompt.'
In this context, the term that fits both forms is likely 'lagger.' As a noun, a lagger is someone who falls behind, similar to a slowpoke or straggler. As an adjective, when someone or something is described as lagger, it indicates that their actions or movements are slow or delayed, aligning with the definition of sluggish. Understanding synonyms and antonyms enhances vocabulary and comprehension for effective communication in English.