Establishment

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use App\Models\Nature;

class Establishment extends Model
{
  //
  public $table = "estabelecimento";
  protected $fillable = ['nmFantasia'];

  public function specialty () {
  return $this->belongsToMany(Specialty::class, 'estabelecimento', 'idUnidade');
  }
}

SearchController

<?php

namespace App\Http\Controllers\Web;

use Illuminate\Http\Request;
use App\Http\Controllers\Controller;
use App\Models\Establishment;
use App\Models\Nature;
use App\Models\Specialty;

class SearchController extends Controller {

  public function search (Establishment $establishment) {
    $search = \Request::get('result');
    if ($search) {
      //$establishmens =  $establishment->all();
      $establishmens =  $establishment::where('nmFantasia', 'like', '%'.$search.'%')->paginate(25);
      return view('web.search', compact ('establishmens') );
    } else {
      return 'Nenhum termo digitado';
    }
  }

  public function teste () {
    $nature = Specialty::where('nmEspecialidade', 'like', '%ATENCAO%')->get()->first();
    echo $nature->nmEspecialidade;

    $unidades = $nature->establishments;
    foreach($unidades as $unidade) {
      echo $unidade->idUnidade;
    }
  }
}

Specialty

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Specialty extends Model
{
  //
  public $table = "especialidade";
  protected $fillable = ['nmEspecialidade'];

  public function establishments () {
  return $this->belongsToMany('App\Models\Establishment', 'especialidade_estabelecimento', 'especialidade_idEspecialidade', 'estabelecimento_idUnidade');
  }

}