According to Samkhya school of thought a word signifies

The correct answer is Vyakti.

To understand why the Sāṃkhya (Samkhya) school holds that a word signifies Vyakti, we need to understand the classical Indian philosophical debate on the meaning of a word (śabdārtha) — one of the most important discussions in Indian linguistics and philosophy of language.

In Indian philosophical grammar and Mīmāṃsā/linguistic thought, there are broadly three candidates for what a word ultimately refers to or signifies:

1. Vyakti (व्यक्ति) — The Individual/Particular Instance
This refers to the specific, concrete, individual object that exists in the world. For example, the word "cow" would signify this particular cow standing in front of you — the unique, individual living being with all its specific properties.

2. Ākṛti (आकृति) — The Form/Shape/Configuration
This refers to the common form, shape, or configuration shared by all members of a class. The word "cow" would signify the cow-shape or the structural pattern (such as the shape of the body, the dewlap, the hump, the hooves, etc.) that is common across all cows.

3. Jāti (जाति) — The Universal/Class-Essence
This refers to the abstract universal — the "cow-ness" (gotva) — the eternal, unchanging, metaphysical essence shared by all cows. This is the position strongly associated with the Mīmāṃsā school (particularly Kumārila Bhaṭṭa) and the Nyāya-Vaiśeṣika school, which hold that the universal (jāti) is the primary referent of a word.

The Sāṃkhya Position — Why Vyakti?
The Sāṃkhya school of thought, with its foundational metaphysics rooted in Prakṛti (primal matter) and its evolutes (vikāras), takes a distinctly particularist and empiricist stance on word-meaning. According to Sāṃkhya:

All manifest reality is made up of Vyakta (the manifest), which refers to the concrete, particular, directly perceivable entities that have evolved out of Prakṛti through the interplay of the three Guṇas (Sattva, Rajas, Tamas). These manifest individuals — the Vyaktis — are what we actually encounter, perceive, and communicate about in everyday experience.

Since Sāṃkhya does not accept eternal, independent universals (Jāti) as real metaphysical entities in the way Nyāya-Vaiśeṣika does, and since it grounds meaning in the concrete, tangible world of Prakṛtic evolution, it holds that a word primarily and directly denotes the individual (Vyakti) — the concrete, particular, manifest thing.

In other words, when we utter the word "cow," according to the Sāṃkhya school, what the word is actually pointing to and referring to is the individual, manifest, concrete cow — not an abstract universal "cow-ness" (Jāti), and not merely a shared structural form (Ākṛti). The individual Vyakti is the real, empirically present entity, and language, for Sāṃkhya, is fundamentally about engaging with that concrete, manifest world.

Contrast with other schools:
— The Mīmāṃsā school (especially Prābhākara Mīmāṃsā, through Śālikanātha) argues that a word signifies Ākṛti (form/configuration).
— The Nyāya-Vaiśeṣika and Kumārila Bhaṭṭa's Mīmāṃsā school argue that a word primarily signifies the Jāti (universal).
— The Sāṃkhya school, rejecting the primacy of abstract universals in favour of the manifest individual, holds that a word signifies Vyakti — the individual/particular.

Therefore, the answer Vyakti correctly reflects the Sāṃkhya school's empirically grounded, particularist philosophy of language, which anchors the meaning of words firmly in the world of concrete, manifest, individual objects — the products of Prakṛti's evolution.