# Synonyms in search

> Synonyms in search allow a search engine to treat different words for the same concept as interchangeable, so a query for 'sneakers' returns the same results as a query for 'trainers' or 'athletic shoes'.

_Source: https://nobi.ai/glossary/synonyms-in-search_

## What is Synonyms in search?

When a shopper types a word that differs from the terms used in product data, synonym rules bridge that gap. Without them, a catalog full of 'trainers' returns nothing when someone searches 'sneakers', even though the products are identical. Synonym handling can be one-way (a maps to b) or two-way (a and b are fully equivalent), and it applies at query time without changing the underlying product data.

## How does synonyms in search work?

- A search engine receives the raw query and checks it against a synonym dictionary or expansion rules.
- Matching words are expanded or replaced with their equivalents before the query runs against the index.
- The engine then retrieves and ranks results as if the shopper had used the catalog's preferred terminology.
- Some systems apply synonyms at index time instead, writing multiple word forms into the index entries themselves.

## Why does it matter?

Shoppers use the language they know, not the language a catalog was built with. Missed synonyms mean missed revenue - a visitor who sees zero results is likely to leave. For dealerships, the same problem appears when a buyer searches 'used trucks' but inventory is labeled 'pre-owned pickups'. Closing those gaps directly lifts conversion without touching product data or ad spend.

[Nobi](https://dashboard.nobi.ai)'s semantic matching reduces the burden of hand-maintaining synonym lists by understanding query intent rather than relying on exact word matches.

## Frequently asked questions

**What is the difference between a synonym and a stemming rule?**
Stemming normalizes word forms - 'running', 'runs', and 'ran' all reduce to the same root. Synonyms map entirely different words to one another, such as 'couch' and 'sofa'. Most search engines apply both techniques independently.

**Should synonyms be one-way or two-way?**
It depends on the relationship. 'TV' and 'television' are true equivalents, so two-way works. But 'dress' and 'gown' are not always the same thing, so a one-way rule - 'gown' expands to also search 'dress' - is safer and avoids surfacing unrelated results.

**How many synonym pairs does a typical ecommerce site need?**
There is no universal answer, but high-traffic sites often maintain hundreds of pairs. The practical starting point is zero-result queries - any search that returns nothing is a candidate for a new synonym rule or a catalog data fix.